The jury is still out on whether or not Facebook advertising actually works well or not. From what I have seen so far it is as I suspected: it works for some (the ones who comprehend HOW to ENGAGE people) and not for others (the ones who are NOT ENGAGING). 
This post on Technobabble has a couple of good examples on the above: Coke and Fox.  Coke does an abysmal job of utilizing Facebook. Just have a look at their page and see for yourself: it is stale, stuffy, and worst of all: not engaging whatsoever. As one Ms Flaitz writes on Coke’s wall: “So, If coca-cola really wants to pretend that it’gets’ facebook….the lame company overview has to go”. Coke doesn’t give their fans any rich content. It’s not like they don’t have any videos, or competitions, or creative Marketing/Advertising people (at least this is what I assume, it being Coca-Cola and all), but they don’t seem to use them. 
Also, they are not involving their fans: Facebook allows you for example to record and post videos INSIDE the platform. How about a user-generated video contest? Or a Facebook application? 
Fox is doing a bit better. Have a look here. 
I really liked this one though: jobsearch-website  Seek’s  Facebook sponsored group. Not only does it give their fans a rich site with videos (their TV ads), it actually gets them involved with a survey, an application they can add to their profile which tells them about new jobs coming up, some advice ressources on how to put together a good CV, and more. This is reflected in the use of this group (e.g. active fans having discussions) and the number of members (3700+ members – over 2000 more than just a week ago). 
All this is pointing to the underlying principle of utilizing Social Media as a Marketing/Communications tool: you need to ENGAGE (with) PEOPLE. That is the only thing that works. The rules of traditional advertising do not apply here. I will keep monitoring advertising on Facebook closely and keep you up-to-date. 

P.S.: I am not a fan of any of the above companies (neither online nor offline)… but I am not averse to the idea of declaring myself a fan of an organization at all. Are you a fan of a sponsored group (company or individual) on Facebook?